Top Speed

So.........I have a hurricane I-4 stock motor, a stock 3 speed and transfer case and 5.38 gears in my 56 cj-5. ( or I will have when I put it back together).
What is top speed and at what rpm for 31 and 33 inch tires? As this build is in it's infancy , now is a good time to plan the drivetrain. :driving:

 

Hit the search, I remember a topic in this section with the same title a couple weeks ago.

And, to answer your question not very fast.

 

shot I had a really good graph on this, I book marked it long time ago...I wonder if i still have it on my other computer....

 

Gear ratio calculator.

http://www.grimmjeeper.com/gears.html

 

Well, it really depends on if you are going up or down hill, how fast the wind is blowing, how much lift you have, and how wide of tires. I have 31x11.5 super swamper bias tires, around 2.5" lift, and am lucky enough to live in a flat area, so with the tach pegged at 3,000 rpm I can hit about 46-48mph, if I want to get daring and run around 3,200 rpm I can do slightly above 50mph, and this is getting between 10 and 12 mpg by the way. On another note: I could only accomplish these speeds after getting the timing/dwell/carb/valves adjusted properly...when I first got the jeep, I was very lucky if I could hit 45mph.

 

yup i had it on my other computer still. heres the link http://www.public.asu.edu/~grover/willys/speed.html

 

is there a drastic difference between the 4 cyl and 6 cyl? i know its like double the hp and a little higher gearing usually

 

I know in mine when I'm doing 45 its seems a lot faster.

 

I know this is a topic people will disagree on. I love the 4 cylinder jeeps and have driven them for decades, but it is my experience that in stock, unrebuilt, condition it is important not to over-rev them. They are a "long stroke" engine meant for endurance rather than speed.

Back in 1956, 50mph was FAST. But in traffic these days it seems impossibly slow. It is real easy to blow up an older jeep motor just trying to keep up. (I've done it...) With the wind noise and tire-howl it's easy to miss the sound of rod bearings going away! The jeep was not a designed as highway vehicle.

I'm not saying that the 4 cylinder is a weak motor, or a that they "can't take it" if in good condition. I know plenty of people here are able to say they trust the Hurricane to take them across the country, and I don't mean to challenge them. I'm just saying on an original motor in a stock jeep, essentially we are talking about an "antique" vehicle and should treat them with TLC.

In my jeeps I feel 45mph is comfortable, 50 is a maximum. With oversize tires, maybe you can add 10% or so.

 

The big diffrence between the 4 and 6 is the HP and the rpm range of the engine. I haven't owned a 4 banger Jeep, but it seems that 3000 rpm is the upper limit, my V6 likes to cruise at 2600. I can pull 4500 for what feels like all day (maybe 10 min up a pass) without a problem. Gearing does help, any engine that can pull 3.73 gears instead of 5.38 will make the jeep faster...

 

50mph / 3200rpm really seems like the sweet-spot with my 62. All stock running on 235/75R15's (about 29" diameter). Any faster and it really sounds like it's really running out of rpm.

I usually towbar it where i'm going to go wheeling if it's further than 10 miles or so. lol

 

My impression is that the gearing is near optimal for the F134 with 5.38s. Any lower (higher numeric) and you run out of revs; any higher (lower numeric) and you run out of power.

I recall that other owners have been able to go a little faster in the F134/5.38 CJs by fitting an overdrive. I think this only gives you a small boost in speed though... Jim (jpflat2a) knows about this, and could comment.

Whatever you do, I think it's fair to say that you will be pushing the envelope of available power with a F134 in a CJ at highway speeds. The power to weight ratio is quite low, considering the aerodynamics of the vehicle. The V6 makes highway driving much easier simply because of the additional power; double the power and you should be able to go half again as fast before you reach the same drag limit.

 

The following excerp is from:
Nearly everthing You Ever Wanted To Know About CJ-3B Speed and The Some

"CJ-3B SUSTAINED SPEED"

Here we are again in the realm of a "rated" calculation.
Below are three charts all based on previously detailed crankshaft velocities.
The main variables are axle ratios and the engine velocity which affects its service life.
All three of the axle ratios shown in the charts will work well with the F-134 engine.
The 4.88 geared axles listed were available on very early military jeeps or some late
CJ-5,6 Jeeps. (65-72)


Speed @ 3200 rpm (maximum recommended rpm)

Axle Ratio 28.5" Tires 29.5" Tires 28.5" Tires 29.5" Tires
with overdrive with overdrive

5.38 49 51 65 68
4.88 54 56 72 75
4.27 62 64 82 85


Speed @ 2700 rpm (compromise crankshaft velocity)

Axle Ratio 28.5" Tires 29.5" Tires 28.5" Tires 29.5" Tires
with overdrive with overdrive

5.38 41 43 55 57
4.88 45 47 61 63
4.27 52 54 69 72


Speed @ 2200 rpm (maximum efficiency)

Axle Ratio 28.5" Tires 29.5" Tires 28.5" Tires 29.5" Tires
with overdrive with overdrive

5.38 34 35 45 46
4.88 37 38 49 51
4.27 42 44 56 58

I like to drive about 62 mph.
That speed is sufficient for me to keep pace in most conditions found locally.
I like the compromise crankshaft velocity of 2700 rpm.
Remember, the Hurricane is not a large cubic inch engine.
Therefore maximum efficient crankshaft velocity may not produce adequate hp.
From this chart I see that using 4.88 ratio axles with overdrive should be near ideal.
Hey this speed of 62 mph is for my CJ-3B, now go find your own.

 

Sorry the charts didn't load very well.

 

The Jeep engine, the go-devil engine, back long long ago when the military was testing the bantam, ford and willys creations, the military chose the willys Jeep for one major reason, most power of the 3. Also, the go devil, which is the basis of the f-head, was tested for 10 hours, under load, on a dyno, at 4,000 RPM. After the engine was done with its 10 hours, it still ran. It was then tore down and inspected. The verdict was that the max lifetime of the engine at 4,000 RPM was 11 hours.

I have good resources, like the actual data notes from the military (borrowed from a friend awhile back)

 

There is a great deal of difference! I had a '64' CJ5 with a Warn overdrive. One day in 1966 I was driving up a hill and was passed by a VW beetle! Ugh. Going over that hill, about all I could make was 40 mph.

A few months later I traded the '64' in for a '67' with the V6. I couldn't believe the difference! The top speed was far faster than you should drive a short wheel base Jeep, and the gas mileage was almost double. I had the 3.63 gears so the overdrive wasn't needed.

Back in the late 60s there used to be a monthly get together of the Las Cruces Jeep club. They had a favorite arroyo that was used as a hill climb test. A couple of the very best drivers could nurse the 4 cly CJ5 up the side of the hill and over the top (barely). Any of us hacks could get the V6 to just fly over the top with no trouble.

The only problem the Jeep dealer had for a couple of years was finding new Jeeps to sell. He was constantly 'out of stock'.

John

 

Thats good to hear because im not far from putting my 67 v6 on the road Although i was content with my 46 2a and the stock flathead with 35" tires when i had it on the road so the 67 might be overkill haha

 

Wow, that was a lot of information. Sounds like a v-6 is the way to go for a normal cruising speed. I haven't driven an early jeep(yet) . How does it handle at 50-60 mph?
Bump steer? Wandering? Kidney shattering ride? Sounds like fun.